Dynamics of active magmatic and hydrothermal systems at Taal Volcano, Philippines, from continuous GPS measurements

[1] A dense network of continuous single- and dual-frequency GPS receivers at Taal Volcano, Philippines, reveals four major stages of volcanogenic deformation: deflation, from installation in June 1998 to December 1998; inflation, from January to March 1999; deflation, from April 1999 to February 2000; and inflation, from February to November 2000. The largest displacements occurred during the February-November 2000 period of inflation, which was characterized by similar to120 mm of uplift of the center of Volcano Island relative to the northern caldera rim at average rates up to 216 mm/yr. Deformation sources were modeled using a constrained least squares inversion algorithm. The source of 1999 deflation and inflation in 2000 were modeled as contractional and dilatational Mogi point sources centered at 4.2 and 5.2 km depth, respectively, beneath Volcano Island. The locations of the inflationary and deflationary sources are indistinguishable within the 95% confidence estimates. Modeling using a running 4-month time window from June 1999 to March 2001 reveals little evidence for source migration. We suggest that the two periods of inflation observed at Taal result from episodic intrusions of magma into a shallow reservoir centered beneath Volcano Island. Subsequent deflation may result from exsolution of magmatic fluids and/or gases into an overlying, unconfined hydrothermal system.